Wood impregnation

ABSTRACT

The present invention relates to a wood-polymer composite, particularly wood which has been impregnated with a mixture containing polymerizable organic compounds, and more particularly to a method for preparing a wood-polymer-composite by impregnating wood material and/or wood-based material with a mixture containing polymerizable organic compounds, and most particularly uses thereof.

[0001] The present invention relates to a wood-polymer composite,particularly wood which has been impregnated with a mixture containingpolymerizable organic compounds, and more particularly to a method forpreparing a wood-polymer-composite by impregnating wood material and/orwood-based material with a mixture containing polymerizable organiccompounds, and most particularly uses thereof.

BACKGROUND OF THE INVENTION

[0002] Wood-polymer composites of this category is based onpolymerization of a monomer in the cavities of the cells (in-situ). Thepolymer produced is usually a thermoplastic (linear polymer). Monomerswhich belong to the vinyl monomer group are the ones usually used forthis purpose. The vinyl monomers used are polymerized by means ofradical chain polymerization. The vinyl monomers are nonpolar, and willtherefore not swell or react with the cell wall of the wood material.Some persons skilled in the art therefore claim that wood-polymermaterials of this type are not <<real>> composites because there is nochemical bonding between the two combined materials. However, there is ahigh extent of infiltration and the material acquires altered physicaland mechanical properties, and hence should be defined as a novel typeof material. Properties which are substantially increased are density,hardness, wear resistance and elastic modulus. Liquid water and watervapor movements in the new material are greatly reduced, especiallyalong the grain. In wood, transport along the grain is many timesgreater than across the grain, but in the new material they are aboutequal. Because the polymer does not react with the structure of the cellwalls, the basic properties of the woody cell wall are not changed.Because the pores of the wood are blocked by polymer, the moisure canonly move within the unchanged woody cell wall, in spaces between thecell wall and the polymer in the lumen, or in any cracks that might bein the material. The time for humidification or drying of cell lumenwood-polymer composites will therefore be 10 to 20 times longer than foruntreated wood. This delay is an advantage in changing environments(especially a spill of liquid water). Because of the longer time, andbecause the polymer may induce a mechanical restraint of swelling, thedimensional stability of the new material is slightly improved. However,this can lead to local stresses in the material, which can result inmicrocracks when the material is subjected to extreme moisturegradients.

[0003] The monomers usually utilized for cell lumen wood-polymercomposite are methyl methacrylate and styrene and unsaturated polyesteroligomers, because of large supply of these chemicals and hence theirlow cost, as well as the relatively simple method of polymerizing them.Negative aspects of methyl methacrylate monomer are its subtantialshrinkage (up to 25%) during polymerization and relatively high vaporpressure (it evaporates easily). Negative aspects of styrene monomer areits high vapor pressure (it evaporates easily) and easily-detectableodour (low odour threshold). A negative aspect of polyester oligomer isits higher viscosity which limits impregnation possibilities.

[0004] Monomer evaporation can lead to a low filling of surfaces bymonomer. Monomer shrinkage can lead to substantail shrinkage and warpingof materials during cure, and can cause voids between polymer and cellwall. By selecting different types of monomers these problems may bereduced.

[0005] One problem of previously known wood-polymer composites of thiscategory is that after impregnation and curing, they continue toliberate vinyl monomers which have an easily-detected odour and whichcan be irritating and injurious to health.

[0006] Other problems of previously known wood-polymer composites arecracking, warping and colour alteration of the materials. These indicatethat temperatures of the curing phase caused by exothermic heat ofreaction have been too high, resulting in excess shrinkage and pyrolysisdamage to the wood. The problem is increased dramatically with increasedcross-sectional size, and in the past has limited the size of materialwhich could be successfully treated.

[0007] Another problem of previously known wood-polymer compositesresults from a combination of moisture in the wood and the curing heat.Because of the exothermic heat of reaction, the temperature, especiallyof larger cross-sections, exceeds the boiling point of water. Thiscauses rapid drying, followed by warping and cracking in moist wood. Forthis reason, previous art successful treatment has been generallylimited to dry (6% moisture content and less) wood.

SUMMARY OF THE INVENTION

[0008] It is the object of the invention to provide a polymerimpregnated wood of higher moisture content and having improvedhardness, which also has low odour, and further, little cracking isobserved in the finished material, thus eliminating the abovedisadvantages.

[0009] Essentially, this object is accomplished by using a wood materialas a starting material having a moisture content from about 3% to about90%, in particular from about 15% to about 35%, especially from about20% to about 30%, and preferably about 25%, and subjecting said startingmaterial to specific polymerizable monomer formulations and impregnationand curing conditions.

[0010] The specific mixture of polymerizable monomers and additivescombined with a specific curing temperature schedule is important forproducing odourless materials.

[0011] When wood-polymer composites are manufactured, moisture may be aproblem, because the reaction exotherm causes temperatures above theboiling point of water in larger cross sections regardless of theheating method used. Rapid dehydration results. This causes deformationsand cracks.

[0012] An essential feature of the present invention is to use startingwood materials having high moisture content. It is not prior knowledgeto produce wood-polymer composites using moist wood as the startingmaterial.

[0013] Wood, including cheap types and scrap material, can be used toproduce noble wood materials such as imitation teak, mahogany, andothers, and also provide them with novel properties like waterresistance and simpler and reduced maintenance requirements. Since themonomers used are colourless, colours can be added, and thereby thefinished product can be coloured throughout

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] According to the present invention, the foregoing and otherobjects are attained by a product, method and uses thereof as disclosedin the patent claims.

[0015] An embodiment of this invention comprises a wood-polymercomposite, characterized by wood impregnated with polymerizable monomersselected from a group consisting of styrene, methylstyrene and tertiarybutylstyrene, initiated with at least three initiators; crosslinked withdivinyl benzene, ethylene glycol dimethacrylate, 1,3-butylene glycoldimethacrylate, ethylene glycol trimethacrylate or trimethylol propanetrimethacrylate and containing oil or wax as a polymerization moderatorand water repellent for the finished product.

[0016] A second embodiment of this invention comprises a method forpreparing a wood-polymer composite by impregnating wood material and orwood-based material, characterized by the steps of:

[0017] utilizing said wood material having a moisture content of fromabout 15 to about 35% based on the weight of said wood material;impregnating said wood material with a composition selected from a groupconsisting of polymerizable mononers, a crosslinker and at least threeinitiators by means of vacuum and/or pressure; and curing saidimpregnated wood material in a hot air oven, steam or hot oil by meansof a temperature sufficient to achieve the desired polymer loading.

[0018] A third embodiment of this invention comprises use ofwood-polymer composite according to any of claims 1 to 9 or asmanufactured according to any of claims 10 to 18, as a doorstep,doorlaminate, floor, handle, building board, pallet, acoustic wood,outdoor furniture, indoor furniture, container floor, play apparatus,benchtop, outdoor deck material, stair and railing material, fencestakes, or timber.

[0019] Particularly, said timber is a railway sleeper, especially anenvironmentally-friendly railway sleeper. Also, said timber can be apole, especially an environmentally-friendly pole.

[0020] However, the use of said wood-polymer composite should not berestricted to those indicated above, but can include generally all kindsof use of wood products.

[0021] To obtain complete cure and low emissions from the finishedproduct, it was found that a combination of initiators is needed. Alower temperature initiator starts the reaction, a second (highertemperature) carries it on and a third (highest temperature) finishesit. In most of these categories, alternative initiators may be used,depending on the reaction conditions, plant safety, cost and end-userequirements. Oil or wax is used to reduce the reaction exotherm duringpolymerization for the larger sizes of material, and also to act aswater repellant for the material. The oil or wax has an additionalbenefit in that it is lower cost than monomer, reducing cost of thetreatment.

[0022] The main monomers (styrene, methylstyrene (particularlypara-methylstyrene) and tertiary butylstyrene) can be used alone or inany combination. The main advantage of methylstyrene and tertiarybutylstyrene is their lower vapor pressure and thus lower emissions inthe production plant and the finished product.

[0023] Quantities of the initiators and crosslinkers used depend onproduct, process and end-use but are between a minimum and maximum valuefor each. Below the minimum value it will not work; above the maximumvalue and the formulation will work but it is unnecessary and costly.Quantity of oil or wax is dependent on product size, curing conditionsand desired end-use properties.

[0024] The mixtures used are shown in Table 1. TABLE 1 Third FourthFifth Second chemical (or chemical (or chemical chemical (or secondthird (or fourth alternate alternate alternate alternate Chemicalchemical chemical) chemical) chemical) Function Styrene MethylstyreneTertiary Main (vinyl toluene) butylstyrene monomers Minimum Maximum %based % based on on monomer monomer 2,2′-Azobis(2- Benzoyl 2,2′-2,2′-Azobis(2- 0.1 0.3 Lower methylbutane- peroxide Azobis(2,4-methylpropane temperature nitrile dimethyl- nitrile initiatorpentaneniitrile 1,1′- 0.1 0.3 Higher azobis(cyano- temperaturecyclohexane- initiator carbonitrile) Tertiary butyl Di-tertiary 0.5 1.5Highest perbenzoate butyl peroxide temperature initiator Di-tertiarybutyl 0.5 1.5 Highest peroxide temperature initiator (for high-temperature curing) Divinyl benzene Ethylene glycol Ethylene1,3-butylene Trimethylol 2 5 Crosslinker dimethacrylate glycoltrimethacrylate glycol propane dimethacrylate trimethacrylate Petroleumoil Vegetable oil Petroleum wax Vegetable wax 0 50 Additive

[0025] The following Examples will further illustrate the invention.

EXAMPLES

[0026] Beech Timbers

[0027] Materials and Methods

[0028] Six beech railway sleepers were used for the experiment. Some ofthese were cut into smaller samples and some were treated whole.

[0029] Type of Wood: Beech (Fagus sylvatica)

[0030] The dimensions of samples from the six beech sleepers were asfollows:

[0031] Small samples: 65×55×280 mm, 96 pieces;

[0032] Medium samples: 55×145×800 mm; 12 pieces;

[0033] Large samples 240×145×800 mm; 3 pieces;

[0034] <<Full scale>>: 240×145×1700 mm; 3 pieces.

[0035] Table 2 shows the dry-density and moisture profile of thesleepers as used in the experiment. As seen in Table 2, the sleepers hadhigh moisture content. There was also great variation in moisturecontent among the sleepers and within each individual sleeper. Each ofthe six parts of Table 2 represent a cross section of an individualsleeper. It was expected that variations in moisture content also wouldbe found in the longitudinal direction of each individual sleeper.Average dry-density of the sleepers was 663 kg/m³±39 kg/m³. TABLE 2Sample number (upper) dry-density in kg/m³ (center) and moisture content(lowest number) of the individual control samples taken from the crosssection of the six sleepers 1 624 33.4% 2 662 30.2% 1 3 5 7 1 3 5 7 611626 629 586 647 653 650 630 27.7% 36.9% 36.1% 31.7% 28.6% 32.3% 30.7%27.9% 2 4 6 8 2 4 6 8 630 621 661 628 652 731 672 660 30.0% 36.2% 37.9%30.7% 25.8% 33.7% 35.5% 27.2% 3 677 30.2% 4 671 27.3% 1 3 5 7 1 3 5 7714 697 687 659 695 708 683 646 30.5% 37.9% 37.1% 25.3% 25.5% 34.6%29.6% 22.3% 2 4 6 8 2 4 6 8 664 666 659 673 708 662 660 604 23.7% 31.2%29.3% 26.4% 24.0% 30.4% 27.4% 24.5% 5 704 38.2% 6 640 28.1% 1 3 5 7 1 35 7 699 679 664 645 660 659 602 609 38.5% 39.6% 33.1% 35.0% 26.3% 27.4%27.2% 27.5% 2 4 6 8 2 4 6 8 806 717 721 702 658 643 638 651 41.0% 41.7%43.1% 33.8% 29.0% 30.7% 28.8% 27.6%

[0036] Impregnation

[0037] For all the treatments, <<full-cell>> impregnation was used. Thewood product was placed in an autoclave and a vacuum of from about 0.01to about 0.03 bar was established for a specific time (t_(V)) prior tofilling the vessel with an impregnating fluid. When the fluid was in,atmospheric pressure was reestablished and then an overpressure of about7.5 bar was produced. The overpressure was maintained for a specifictime (t_(P)).

[0038] Curing

[0039] All curing of monomer was carried out in a hot air oven havingset temperatures of 70 and 140° C. Because the oven had residual heat inthe heating elements, the temperature rose to 80° C. after operation ofseveral hours at a set temperature of 70° C. Nevertheless, thetemperature of the curing is referred to as 70° C.

[0040] Completed Treatments and Evaluations Thereof

[0041] Twenty-five different treatments were carried out Each treatmentwas varied as regards the size of the wood materials, proportion ofchemicals in the mixture, time of vacuum and pressure during theimpregnating processes, as well as temperature and time of the curingprocesses. Four steps of the test were completed. A short descriptionand evaluation of them is outlined hereinafter.

[0042] Step 1

[0043] Step 1 is comprised of sixteen different treatments of six smallsamples of each individual treatment. A sample from each sleeper wasused such that variation of the wood materials of the differenttreatments were distributed as evenly as possible. These sixteentreatments were the basis for evaluation of impregnating quality, aswell as evaluation of chemistry and curing completeness. Different timesof vacuum and pressure were used. These are summarized in Table 3, Thetreatments can be divided into four main groups; a: treatment 1-4, b:treatment 5-8, c: treatment 9-12, d: treatment 13-16.

[0044] Group a

[0045] Group a was treated using the first chemical formula. Time ofvacuum was short, 5-8 min. Time of pressure was varied from 5 to 18 min.Time of curing at 70° C. was varied from 3 to 6.5 h. Time of post-curingat 140° C. was about 4 h. The conversion level of these treatments waslow, thus indicating high evaporation of monomer during the curingprocess. Exothermic heat of reaction was not observed, indicating thatthe polymerization was not complete. No odour after completed curing wasrecognized, indicating very low values of residual monomer. As thesamples dried, they shrank. The drying was severe, so it produced cracksin the materials. Residual moisture was estimated to be 0%.

[0046] Group b

[0047] After evaluation of group a, the concentration of initiator inthe monomer mixture was increased. This was an attempt to initiatecuring earlier. Time of vacuum was prolonged to 11-15 min. Time ofpressure was varied from 4 to 19 min. Time of curing at 70° C. wasvaried from 6 to 10 h. Time of post-curing at 140° C. was 6 h. Thesamples were cooled before post-curing. During the longer curing time at70° C., exothermic heat of reaction was detected, For treatments numbers6, 7 and 8 this was observed after 7 h wherein the core temperature ofthe materials exceeded the surface temperature of the samples. No odourafter completed post-curing at 140° C. was recognized. Moisturereduction and crack formation were the same as observed for group a.

[0048] Group c

[0049] After evaluation of group b, curing at 70° C. without post-curingwas done. The same chemical formula as for group b was used. Time ofcuring at 70° C. was prolonged to 17-20 h to observe when the exothermicreaction occurred and how high the core temperature became. The coretemperature exceeded the surface temperature after 5-7 h with a maximumoccuring after 8.5-11 h. Time of vacuum was slightly reduced to 8.5-11min. Time of pressure was varied from 4.5 to 28 min. Measuring was doneafter curing at 70° C. The odour was <<medium>> after curing at 70° C.This indicated residual monomers which have not reacted. To obtainconsistent evaluation of polymer uptake, the samples were laterpost-cured at 140° C., but this is not reported in Table 3.

[0050] Group d

[0051] After evaluation of group c, it was decided to use anotherinitiator in an attempt to start polymerization at an earlier stage andpossibly increase conversion. For this group, measurements andevaluation were made after curing at 70° C. Post-curing at 140° C. wascarried out at a later stage to obtain consistent evaluation of polymeruptake and conversion. Time of vacuum was reduced to 5-12 min. Time ofpressure was varied from 0.5 to 4.5 min. Time of curing at 70° C. wasvaried from 10 to 12 h. Dramatically shortening of the curing processwas observed. The time until the core temperature exceeded the surfacetemperature was about 2 h, and the maximum temperature was observedaccording to 4.5 to 5 h. This effected the odour after treatment. Theodour was classified as <<low>> which indicates a high level ofconversion. Calculated conversion rose dramatically from 72% for groupsa-c to 88% for group d. The new initiator was successful in reducing thereaction time and increasing conversion.

[0052] Step 2

[0053] Step 2 is comprised of three individual treatments of sleepers 1,2 and 3, Details are given in Table 4, treatment numbers 17, 18 and 19.

[0054] Time of vacuum was varied from 11 to 14.5 min., and time ofpressure was varied from 2.5 to 6.3 min. For the three treatments,temperature of the oven stabilized at 76 to 82° C. This was held for 18h. The samples had a zone about 4 mm deep on the surface which had lowpolymer content, indicating monomer evaporation.

[0055] Half of all samples of step 2 were post-cured at 140° C. for 20h. This produced greater shrinkage, deformation and internal cracks inthe materials. In addition, the core was dark brown as a result of thehigh temperature during such a long time. The internal cracks were notvisible at the surface. The cracks had the same appearance as thoseproduced by drying wood using conditions that are too severe.Post-curing resulted in a residual moisture of 0%. It is not possible tonotice any odour from the materials and residual monomers were thereforeconsidered to be at a very low level. This demonstrates the chemicalmixture clearly affects the result.

[0056] Step 3

[0057] Step 3 was comprised of three individual treatments of largesamples (full cross section) of sleeper 1, 2 and 3. Details are given inTable 4, treatments numbers 20, 21 and 22. Time of vacuum was variedfrom 5 to 7.5 min. For the three treatments temperature of the ovenstabilized at 84 to 88° C. This was held for 19-22 h.

[0058] Step 4

[0059] Step 4 was comprised of three individual treatments of <<fullscale>> samples of sleepers 4, 5 and 6. Details are given in Table 4,treatments numbers 23, 24 and 25. Time of vacuum was varied from 18 to23 min. and time of pressure was varied from 8 to 9.5 min. For the threetreatments, temperature of the oven stabilized at 86 to 88° C. This washeld for 19-23 h. TABLE 3 Summary of treatments 1-16 Treatment No: 1 2 34 5 6 7 8 Samples small small small small small small small small Number6 6 6 6 6 6 6 6 Impregnating Wood Beech Beech Beech Beech Beech BeechBeech Beech Moisture measur. measur. measur. measur. measur. measur.measur. measur. Density measur. measur. measur. measur. measur. measur.measur. measur. Vacuum 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Pressure7 7 7 7 7 7 7 7 Time vacuum <0.1 bar (min.) 5.2 6.7 6.3 7.8 11.2 11.613.1 14.9 Time pressure >7 bar (min.) 4.8 8.2 17.5 18.7 3.7 7.5 16.819.4 lot time process (min.) 26 29.9 37.3 41.0 28.0 32.8 44.0 48.5Curing Heat source oven oven oven oven oven oven oven oven Temperature 174 76 76 76 76 78 80 80 Temperature 2 136 140 140 140 136 140 140 140Time temp 1 (h) 3 4.4 5.1 6.4 6 7.5 8.1 9.8 Time temp 2 (h) 4.2 4.2 4.24.2 6 6 6 6 Chemicals Vinyl-toluene  58.0%  58.0%  58.0%  58.0%  58.0% 58.0%  58.0%  58.0% Styrene  25.5%  25.5%  25.5%  25.5%  25.5%  25.5% 25.5%  25.5% Oil  16.5%  16.5%  16.5%  16.5%  16.5%  16.5%  16.5% 16.5% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% DVB (63%) 3.10%  3.10%  3.10%  3.10%  3.10%  3.10%  3.10%  3.10% 1,1′-azobis(tyclohexane-  0.20%  0.20%  0.20%  0.20%  0.35%  0.35%  0.35%  0.35%carbonitrile) DTBP (98%)  0.30%  0.30%  0.30%  0.30%  0.30%  0.30% 0.30%  0.30% 2,2′-azobis (2,4 dimethyl- pentanenitrile) MeasurementsMoisture   25%   25%   25%   25%   24%   24%   24%   24% weight (1) g725 775 756 819 742 794 735 762 weight (2) g 1015 1083 1107 1157 10951129 1060 1096 weight (3) g 986 1013 934 967 weight (4) g 787 858 862882 852 869 828 846 Calculations Monomer loading  50.0%  49.7%  58.0% 51.6%  59.0%  52.3%  54.8%  54.4% Polymer loading  35.7%  38.4%  42.5% 34.6%  42.4%  35.7%  39.7%  37.7% Level of conversion  71.4%  77.3% 73.3%  67.1%  71.8%  68.3%  72.4%  69.3% Hardness 1 4.5 4.8 5.0 4.6 4.45.4 5.2 4.5 Hardness 2 (4 mm into sample) 4.2 6.3 7.4 7.0 5.7 7.0 6.87.1 Hardness control pr 3.3 3.4 3.1 3.3 3.1 3.5 3.1 3.1 Hardnessimprovement: % HB 1   36%   41%   61%   39%   42%   54%   68%   45%Hardness improvement: % HB 2   27%   85%   139%   112%   84%   100%  119%   129% Evaluation Odour no odour no odour no odour no odour noodour no odour no odour no odour Colour golden golden golden goldengolden golden golden golden Treatment No: 9 10 11 12 13 14 15 16 Samplessmall small small small small small small small Number 6 6 6 6 6 6 6 6Impregnating Wood Beech Beech Beech Beech Beech Beech Beech BeechMoisture measur. measur. measur. measur. measur. measur. measur. measur.Density measur. measur. measur. measur. measur. measur. measur. measur.Vacuum 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Pressure 7 7 7 7 7 7 7 7Time vacuum <0.1 bar (min.) 8.6 8.6 10.1 10.8 6.3 4.9 5.2 11.9 Timepressure >7 bar (min.) 4.5 9.0 13.8 28.0 0.4 4.1 0.4 4.5 lot timeprocess (min.) 28.0 31.7 37.7 54.1 19.4 24.3 23.9 31.3 Curing Heatsource oven oven oven oven oven oven oven oven Temperature 1 80 82 82 8280 80 80 80 Temperature 2 0 0 0 0 0 0 0 0 Time temp 1 (h) 17 17.6 1919.8 10 10.5 11.6 12.2 Time temp 2 (h) 0 0 0 0 0 0 0 0 ChemicalsVinyl-toluene  58.0%  58.0%  58.0%  58.0%  58.0%  58.0%  58.0%  58.0%Styrene  25.5%  25.5%  25.5%  25.5%  25.5%  25.5%  25.5%  25.5% Oil 16.5%  16.5%  16.5%  16.5%  16.5%  16.5%  16.5%  16.5% 100.0% 100.0%100.0% 100.0% 100.0% 100.0% 100.0% 100.0% DVB (63%)  3.10%  3.10%  3.10% 3.10%  3.10%  3.10%  3.10%  3.10% 1,1′-azobis (tyclohexane-  0.35% 0.35%  0.35%  0.35%  0.20%  0.20%  0.20%  0.20% carbonitrile) DTBP(98%)  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%2,2′-azobis (2,4 dimethyl- 0.125% 0.125% 0.125% 0.125% pentanenitrile)Measurements Moisture   20%   20%   20%   20%   16%   16%   16%   16%weight (1) g 724 746 732 780 701 712 685 713 weight (2) g 1040 1061 10741115 1071 1073 1022 1066 weight (3) g 926 937 938 968 956 1002 947 999weight (4) g 850 870 862 876 928 938 888 924 Calculations Monomerloading  52.4%  50.7%  56.1%  51.5%  61.2%  58.8%  57.1%  57.4% Polymerloading  40.9%  39.9%  41.3%  34.8%  53.6%  52.8%  50.4%  50.3% Level ofconversion  78.1%  78.8%  73.7%  67.5%  87.5%  89.8%  88.3%  87.6%Hardness 1 4.5 4.4 4.6 4.5 5.3 5.7 5.1 5.2 Hardness 2 (4 mm into sample)8.7 7.3 5.6 7.5 10.0 8.9 9.7 9.6 Hardness control pr 3.3 3.4 3.1 3.3 3.13.5 3.1 3.1 Hardness improvement: % HB 1   36%   29%   48%   36%   71%  63%   65%   68% Hardness improvement: % HB 2   164%   115%   81%  127%   223%   154%   213%   210% Evaluation Odour medium medium mediummedium low low low low Colour dry dry dry dry malt/dry malt/dry malt/drymalt/dry

[0060] TABLE 4 Summary of treatments 17-25 Step 2 Step 3 Step 4Treatment No: 17 18 19 20 21 22 23 24 25 Samples medium medium mediumfull c.s. full c.s. full c.s. full c.s. full c.s. full c.s. Number 4 4 4Impregnating Type of wood Beech Beech Beech Beech Beech Beech BeechBeech Beech Vacuum 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Pressure7 7 7 7 7 7 7 7 7 Time vacuum <0.1 bar (min.) 14.4 10.9 11.2 16.1 17.511.2 20.3 18.2 22.8 Time pressure >7 bar (min.) 6.3 2.5 6.0 7.7 5.6 4.99.5 7.7 8.8 lot time process (min.) 36.4 25.2 28.4 34.0 34.7 26.6 39.635.7 42.0 Curing Heating source oven oven oven oven oven oven oven ovenoven Temperature 1 77 76 82 88 88 84 86 86 88 Temperature 2 0 0 0 0 0 00 0 0 Time temp 1 (timer) 18 18 18 22 20 19 23 21 19 Time temp 2 (timer)0 0 0 0 0 0 0 0 0 Chemicals Vinyl-toluene  58.0%  58.0%  58.0%  58.0% 58.0%  58.0%  58.0%  58.0%  58.0% Styrene  25.5%  25.5%  25.5%  25.5% 25.5%  25.5%  25.5%  25.5%  25.5% Oil  16.5%  16.5%  16.5%  16.5% 16.5%  16.5%  16.5%  16.5%  16.5% 100.0% 100.0% 100.0% 100.0% 100.0%100.0% 100.0% 100.0% 100.0% DVB (63%)  3.10%  3.10%  3.10%  3.10%  3.10% 3.10%  3.10%  3.10%  3.10% 1,1′-azobis (cyclohexane-  0.20%  0.20% 0.20%  0.20%  0.20%  0.20%  0.20%  0.20%  0.20% carbonitrile) DTBP(98%)  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%2,2′-azobis (2,4 dimethyl- 0.125% 0.125% 0.125% 0.125% 0.125% 0.125%0.125% 0.125% 0.125% pentanenitrile) Measurements Moisture  11.5%   15%  13%   28%   25%   25%   22%   33%   23% weight (1) kg 3.81 4.4 4.3320.2 21 21.2 43 46 39 weight (2) kg 5.88 6.3 6.07 30.5 30.5 28.5 57.5 5858.5 weight (3) kg 5.47 5.78 5.72 28.6 28.4 26.3 54.5 55.5 56Calculations Monomer loading  61.0%  50.0%  45.0%  65.0%  57.0%  43.0% 41.0%  35.0%  62.0% Polymer loading  52.0%  40.0%  40.0%  57.0%  48.0% 34.0%  36.0%  31.0%  57.0% Level of conversion  86.0%  79.0%  87.0% 87.0%  85.0%  79.0%  88.0%  91.0%  93.0% Evaluation Odour low low lowlow low low low low low Colour dry dry dry dry dry dry dry dry dry

[0061] Monomer and Polymer Loading and % Conversion of Monomer toPolymer

[0062] Monomer and polymer loading, and conversion for the differenttreatments are given in Table 5, Table 6 and Table 7. TABLE 5 Monomerand polymer loading and conversion of monomer to polymer for the smallsamples After After Before imp. curing Treatment imp. weight weight McConver- No weight (g) (g) (g) imp ML PL sion 1 725 1015 787 18% 47% 28%59% 56 43 32 6% 11% 4% 2 775 1083 858 21% 49% 34% 70% 42 50 42 8% 12%10% 3 756 1107 863 25% 58% 42% 73% 41 34 49 9% 8% 10% 4 819 1157 882 31%55% 42% 76% 70 14 50 5% 13% 14% 5 742 1095 852 23% 59% 41% 71% 40 33 596% 8% 13% 6 794 1129 869 29% 55% 41% 75% 83 15 37 11% 13% 10% 7 735 1060828 24% 55% 40% 73% 71 65 40 8% 17% 11% 8 762 1096 846 24% 55% 38% 69%95 41 32 9% 15% 9% 9 724 1040 850 18% 51% 38% 75% 31 37 37 3% 8% 7% 10746 1061 870 16% 50% 36% 72% 61 55 43 2% 15% 11% 11 732 1074 862 21% 57%42% 75% 34 54 40 2% 13% 9% 12 780 1115 876 25% 54% 41% 75% 39 20 38 5%9% 10% 13 701 1071 928 16% 62% 54% 88% 36 30 42 5% 9% 10% 14 713 1073938 16% 59% 52% 89% 53 47 22 8% 9% 8% 15 685 1022 888 16% 57% 51% 88% 4590 74 4% 20% 16% 16 713 1066 924 16% 58% 51% 88% 74 44 37 6% 14% 11%

[0063] TABLE 6 Monomer and polymer loading and conversion of monomer topolymer for the medium-sized samples PL Weight Weight 70° C. TreatmentWeight after cured (3% Conv. no. Samp. no. before kg kg 70° C. MC ML mc)70° C. 17 1B1 3.61 5.81 5.42 11% 68% 59% 87% 1B2 3.91 6.04 5.60 12% 61%52% 85% 1B3 4.02 6.06 5.62 12% 57% 48% 84% 1B4 3.68 5.59 5.24 11% 57%50% 87% Average 3.81 5.88 5.47 11% 61% 52% 86% 18 2B1 4.52 6.28 5.67 14%44% 32% 73% 2B2 4.61 6.49 5.89 18% 48% 36% 75% 2B3 4.48 6.38 5.87 16%49% 39% 80% 2B4 3.97 6.05 5.68 11% 58% 51% 88% Average 4.40 6.30 5.7815% 50% 40% 79% 19 3B1 4.31 5.57 5.22 13% 33% 27% 82% 3B2 4.53 6.44 6.0314% 48% 41% 86% 3B3 4.45 6.39 6.00 13% 49% 43% 87% 3B4 4.02 5.89 5.6110% 51% 47% 91% Average 4.33 6.07 5.72 13% 45% 40% 87%

[0064] TABLE 7 Monomer and polymer loading and conversion of monomer topolymer for the large samples Treat Samp. Weight before Weight afterWeight cured PL 70° C. No. Length No. kg kg kg MC ML (3% mc) Conv. 20 1c20.2 30.5 28.6 28% 65% 57% 87% 21  80 cm 2c 21.0 30.5 28.4 25% 57% 48%85% 22 3c 21.2 28.5 26.3 25% 43% 34% 79% 23 4c 43.0 57.5 54.5 22% 41%36% 88% 24 170 cm 5c 46.0 58.0 55.5 33% 35% 31% 91% 25 6c 39.0 58.5 56.023% 62% 57% 93%

[0065] Hardness of wood and the wood-polymer composite made from it isgiven in Table 8. TABLE 8 Changes in Brinell-scale (HB) hardness as aresult of the treatments HB HB HB % increase % increase Treatment NoControl The surface 4 mm HB-surface HB-4 mm 1 3.3 4.5 4.2 36% 26% 2 3.44.8 6.3 41% 85% 3 3.1 5.0 7.4 64% 141% 4 3.3 4.6 7.0 40% 115% 5 3.1 4.45.7 41% 80% 6 3.5 5.4 7.0 52% 97% 7 3.1 5.2 6.8 68% 119% 8 3.1 4.5 7.147% 133% 9 3.3 4.5 8.7 37% 162% 10 3.4 4.4 7.3 29% 115% 11 3.1 4.6 5.649% 81% 12 3.3 4.5 7.5 38% 129% 13 3.1 5.3 10.0 67% 216% 14 3.5 5.7 8.962% 150% 15 3.1 5.1 9.7 65% 211% 16 3.1 5.2 9.6 70% 215%

[0066] Pine Timbers

[0067] Wood Species: Scots Pine (Pinus sylvestris)

[0068] Materials and Methods

[0069] Ten sleepers were received and their moisture content (MC) andheartwood/-sapwood location mapped for each sleeper. Each sleeper wasweighed just before impregnation, after impregnation and after curing.MC was measured by cutting cores, separating them into increments,weighing each increment, ovendrying the increments and weighing themagain. This method gave MC at various positions within each sleeper.

[0070] A 60 parts to 40 parts mixture of para-methyl styrene to styrenewas the base monomer used. Based on the weight of this base monomer, thefollowing ingredients were added: 20% mineral oil (reaction moderatorand water repellant), 3.5% divinyl benzene (crosslinker), 0.5%2,2′-azobis (2-methyl-butanenitrile) (low-temperature initiator), 0.2%1,1′-azobis (cyclohexane-carbonitrile) (medium-temperature initiator)and 0.5% teriary butyl perbenzoate (high-temperature initiator).

[0071] Impregnation was carried out on all sleepers using vacuum for ½hour, admitting monomer and then pressure of 5.3 bar. Pressure time forsleepers 1, 4 and 9 was ½ hour, for 2, 5, 6, 7 and 10 it was 1 hour andfor sleeper 8 pressure time was 3 hours.

[0072] Curing was carried out in a chamber 300 mm larger in alldimensions than a single sleeper. Temperature of the curing chamber, thesurface of the sleeper and at locations within the sleeper was measuredas curing took place, Sleepers were treated and cured individually,except for the last two, which were processed together throughout.

[0073] Since rather severe internal checking ocurred in the sapwoodportions of some of the first few sleepers treated, the curingtemperature was controlled in some subsequent sleepers to try todecrease this checking.

[0074] After curing, cross-sections were cut from each sleeper inlocatoions where temperature had been measured, and polymer contentassessed for the section. MC of the heartwood was also measured at thattime using cores. One sleeper was sawed longitudinally and densitieswere measured sequentially in sapwood, outer heartwood and innerheartwood for 1 m along the length.

[0075] Samples 50 m square in cross section and 150 mm long wereprepared from untreated sapwood and heartwood, from treated heartwood,and from treated sapwood with and without internal checking. They wereloaded perpendicular to the grain, parallel to the annual rings(tangentially), which is the same direction a rail plate would loadthem. The testing machine recorded load and displacement (measured byLVDT) in a datalogger. The area was 50 mm by 50 mm, in the center of thesample.

[0076] Completed Treatments and Evaluations Thereof

[0077] MC Just Before Treating

[0078] Moisture contents determined at the time of treating are given inTable 9. TABLE 9 Representative MC just before treatment Sleeper #Surface Mld Sap Deep Sap Outer Heart Inner Heart 1 27.7% 105.8%  122.7% 82.6% 30.3% 2 21.9% 30.6% 37.6% 28.8% 27.0% 3 18.5% 23.7% 25.6% 27.1%25.1% 4 19.5% 33.5% 27.7% 26.2% 26.8% 5 24.8% 56.1% 33.0% 18.6% 28.8% 624.2% 33.6% 44.5% 32.6% 27.1% 7 20.8% 26.9% 28.1% 28.8% 29.1% 8 15.3%16.3% 16.2% 24.2% 28.1% 9 19.4% 28.4% 26.7% 25.3% 27.6% 10 14.0% 16.6%20.2% 23.5% 25.2% Avg 20.6% 37.2% 38.2% 31.8% 27.5%

[0079] Sapwood penetration by monomer of all sleepers except number 1was good because their MC was in the treatable range, Sapwoodpenetration of sleeper number 1 was limited to the drier shell, with thewetter sapwood not penetrated. Even so, overall uptake was similar toother sleepers.

[0080] Curing Quality

[0081] All sleepers cured and there was virtually no odour after coolingto room temperature. Pre-existing surface checking expanded very littleand no new checks appeared.

[0082] Monomer in heartwood cured. This was determined by lack of smelland hardness values equivalent to wood-polymer composites, and not thelower values of untreated wood.

[0083] Internal checks in sapwood were minimized when curing temperaturewas moderated and when moisture content and sapwood depth were lower.The effect of curing temperature is shown in Table 10. TABLE 10 Maximumtemperatures reached in sleeper, and effect on checking Sleeper # (insequence Shallow Deep Shallow treated) Surface Sap Sap Heart HeartDetails Checking 4 113.1 — — — 133.6 9 107.2 119.5 — — 98.5 1 99.5 97.877.6 — — Sleeper mostly Little checking sapwood, because of limitedlimited penetration penetration because of high MC 2 101.5 109.8 115.7 —119.2 Considerable checking 7 111.4 115.3 125.1 — 98.6 Considerablechecking 5 125.0 110.9 113.8 — 103.0 Considerable checking 8 99.6 99.698.1 — 87.5 Maximum Little checking temperature limited 6 98.8 101.3116.4 — 83.9 Cured with 10 Smaller and fewer checks 10 98.8 101.3 116.490.9 83.9 Maximum Smaller and temperature fewer checks limited, sleepermostly heartwood

[0084] Monomer and Polymer Loading

[0085] Table 11 summarizes the loading results. TABLE 11 Monomer andpolymer loading of treated sleepers Unloaded Monomer Polymer WeightSleeper # (kg) Loading (kg) Loaded (kg) Loss (kg) Loss 1 55.57 24.0421.77 2.27 9.4% 2 39.35 20.86 19.16 1.70 8.2% 4 39.55 21.46 20.1 1.366.3% 5 38.56 16.44 14.85 1.59 9.7% 6 47.74 21.09 19.28 1.81 8.6% 7 45.9315.53 15.08 0.45 2.9% 8 49.10 14.63 13.04 1.59 10.9% 9 37.78 16.65 14.382.27 13.6% 10 46.38 11 9.98 1.02 9.3% Averages 17.97 16.40 1.56 8.8%

[0086] Average monomer loading of the nine sleepers was about 22 kg. Theweight loss during cure was about 2 kg per sleeper or about 9% of themonomer weight. Since high temperatures, some above boiling point ofwater, were reached during cure, some of the weight loss must be water.Thus the 2 kg weight loss from a sleeper is partly water and partlymonomer. If it were all monomer loss, another way to express would bethat the monomer to polymer conversion was 91%, which is slightly higherthan for the best beech sleeper treatment.

[0087] Loading of Sapwood, Heartwood and Different Locations and MCs

[0088] Polymer loading for different parts of the sleepers werecalculated from density measurements made from pieces cut from them.Nearly all available space was filled by polymer in sapwood, givingdensities just greater than 1 g/cc (average 1.03 g/cc). Heartwoodloading was greatest near sleeper ends and around cracks, and decreasedwith distance from the sleeper end, becoming zero about 30 cm from theend. Polymer in heartwood was mostly in latewood and maximum loadingswere near 50% of available space (average density of 0.72 g/cc).

[0089] Any sapwood below about 30% MC treated well and all heartwood MCwas suitable for treating when the sleepers were received.

[0090] Quality

[0091] There were surface checks present before treatment. Theseenlarged slightly during treatment. Sapwood shrunk somewhat more thanheartwood, producing some rounded (2 to 3 mm) surfaces. No warpingoccured. Sleeper appearance was good.

[0092] Compression Strength and Stiffness

[0093] The values of untreated and treated sleepers are reported inTable 12. TABLE 12 Stiffness and yield stress (MPa), density (g/cc) andpolymer uptake of WPC and the untreated wood from which it was madeTreatment Yield stress MOE Density Uptake Untreated pine heartwood 6 4090.48 — Untreated pine sapwood 5 991 0.54 — Pine heartwood WPC 12 10580.74  51% Pine sapwood WPC 50 3087 1.04 100% Checked pine sapwood WPC 17960 1.02  98%

[0094] Since stiffness (MOE) and yield stress (load at which thematerial begins to crush) are mostly determined by earlywood propertieswhen loading is in the tangential direction, and since heartwood WPCpolymer is found mostly in latewood, it is expected that heartwood WPCproperties would be similar to untreated wood as is indicated in thetable. The high loading of sapwood WPC (reflected in high densities)increased strength and stiffness greatly. Sapwood yield stress and MOEvalues are about the same as values for treated hardwoods like birch.

[0095] These results indicate that resistance to compressive loading andto mechanical wear should be noticeably better in WPC sleepers than inthe wood from which it was made.

1. Wood-polymer composite, characterized by wood impregnated withpolymerizable monomers selected from a group consisting of styrene,methylstyrene and tertiary butylstyrene, initiated with at least threeinitiators; crosslinked with divinyl benzene, ethylene glycoldimethacrylate, 1,3-butylene glycol dimethacrylate, ethylene glycoltrimethacrylate or trimethylol propane trimethacrylate and containingoil or wax as a polymerization moderator and water repellent for thefinished product.
 2. Wood-polymer composite according to claim 1,characterized in that said monomers are styrene, para-methyl styrene,tertiary butylstyrene and combinations thereof.
 3. Wood-polymercomposite according to claim 1, characterized in that said initiatorsare selected in the following manner: at least one initiator is selectedfrom a low temperature class initiator of 2,2′-azobis(2-methyl-butanenitrile), benzoyl peroxide, 2,2′-azobis(2,4-dimethyl-pentanenitrile), 2,2′-azobis (2-methyl-propanenitrile); atleast one initiator is selected from a medium temperature classinitiator of 1,1′-azobis (cyclohexane-carbonitrile) and 1,1′-azobis(cyanocyclohexane-carbonitrile); and at least one initiator is selectedfrom a high temperature class initiator of tertiary butyl perbenzoateand di-tertiary butyl peroxide.
 4. Wood-polymer composite according toclaim 1, characterized in that said polymerizable monomers presented aspolymerized monomers are distributed throughout the whole of saidcomposite, or within a shell below the exterior surfaces and ends 2 mmdeep and deeper.
 5. Wood-polymer composite according to any of thepreceding claims, characterized in that said composite containing saidpolymerized monomers has a density of from about 0.8 g/cc to about 1.2g/cc.
 6. Wood-polymer composite according to any of the precedingclaims, characterized in that said composite untreated with saidpolymerizable monomers has an average moisture content from about 3 toabout 90%, and the moisture content of said composite treated with saidpolymerizable monomers is from about 0 to about 50%.
 7. Wood-polymercomposite according to any of the preceding claims, characterized inthat said composite is a round, sawn or laminated wood product. 8.Wood-polymer composite according to claim 7, characterized in that saidwood product is a railway sleeper, especially anenvironmentally-friendly railway sleeper.
 9. Wood-polymer compositeaccording to claim 7, characterized in that said wood product is a pole,especially an environmentally-friendly pole.
 10. Method for preparing awood-polymer composite by impregnating wood material and/or wood-basedmaterial, characterized by the steps of: utilizing said wood materialhaving a moisture content of from about 15 to about 35% based on theweight of said wood material; impregnating said wood material with acomposition selected from a group consisting of polymerizable monomers,a crosslinker and at least three initiators by means of vacuum and/orpressure; and curing said impregnated wood material in a hot air oven,steam or hot oil by means of a temperature sufficient to achieve thedesired polymer loading.
 11. Method according to claim 10, characterizedin that said moisture content is about 25%.
 12. Method according toclaim 10, characterized in that said temperature of said hot air oven isfrom about 70 to about 140° C., preferably the temperature is about 70°C.
 13. Method according to claim 10, characterized in that saidpolymerizable monomers are selected from the group consisting ofstyrene, methylstyrene and tertiary butylstyrene.
 14. Method accordingto claim 10, characterized in that said crosslinker is divinyl benzene,ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate,ethylene glycol trimethacrylate, or trimethylol propane trimethacrylate.15. Method according to claim 10, characterized in that impregnation isinitiated with three initiators selected from low, medium and hightemperature classes, wherein at least one initiator is selected from alow temperature class initiator of 2,2′-azobis (2-methyl-butanenitrile),benzoyl peroxide, 2,2′-azobis (2,4-dimethyl-pentanenitrile), 2,2′-azobis(2-methyl-propanenitrile), wherein at least one initiator is selectedfrom a medium temperature class initiator of 1,1′-azobis(cyclohexane-carbonitrile) and 1,1′-azobis(cyanocyclohexane-carbonitrile), and wherein at least one initiator isselected from an initiator of high temperature class of tertiary butylperbenzoate and di-tertiary butyl peroxide.
 16. Method according toclaim 10, characterized in that time of impregnation is from about 15 toabout 45 minutes.
 17. Method according to claim 10, characterized inthat time of curing is from about 2 to about 12 h.
 18. Method accordingto claim 17, characterized in that time of curing is about 8 h.
 19. Useof wood-polymer composite according to any of claims 1 to 9 or asmanufactured according to any of claims 10 to 18, as a doorstep,doorlaminate, floor, handle, building board, pallet, acoustic wood,outdoor furniture, indoor furniture, container floor, play apparatus,benchtop, outdoor deck material, stair and railing material, fencestakes, or timber.
 20. Use according to claim 19, wherein the timber isa railway sleeper, especially an environmentally-friendly railwaysleeper.
 21. Use according to claim 20, wherein the timber is a pole,especially an environmentally-friendly pole.